The purpose of the proposed research project will be to study the biological capabilities and molecular biology of cell-to-cell communication between cells in culture. In preliminary studies we have indications that information related to hormonal stimulation can be transferred between co-cultured mouse ventricular myocardial cells and rat ovarian granulosa cells by cell-to-cell communication presumably via gap junctions. These experiments show that upon exposure of the co-cultures to a hormone specific for one cell type, a response is elicited from the second cell type. We propose to characterize further this co-culture system pharmacologically, physiologically, and cytologically in order to completely define the nature of the hormonal responses that are transmitted by junctional communication. The hormonal responses of both myocardial and granulosa cells appear to be mediated by cyclic AMP. Thus, cyclic AMP is a possible candidate as the "communicator" of hormonal stimulation in this system. Therefore, we plan to examine cyclic AMP levels in both cell types with radioimmunoassay procedures, and attempts will be made to localize this substance with immunohistochemical and autoradiographic methods. These studies will be designed to yield qualitative and quantitative information on the transmitted "communicator". Similar co-culture approaches will be utilized to study the possible role of cell-to-cell communication in other cell systems that are capable of hormone responses and/or cell differentiation in culture. The ultimate objective will be to utilize this approach to develop a novel methodology for examining the role of cell-to-cell communication in intact tissues where cell interactions are essential for both differentiation and normal physiological processes.